An American doctor flew to Kenya in the early 1960s to prove that a people living on milk, meat and blood would have the worst hearts on earth, and found 400 men without a sign of heart disease between them. George Mann was a Vanderbilt professor who had helped set up the Framingham study, and he was not a crank. The theory of the day said that saturated fat raised cholesterol and cholesterol furred the arteries, and the Masai of the Rift Valley were the perfect test, because they ate almost nothing else. A warrior lived on milk, several litres of it a day, fresh or soured. He ate meat at feasts and on raids. When a bullock was needed and not to be killed, he opened a vein in its neck, drew off a gourd of blood, and drank that mixed with the milk. Vegetables were for women and the sick. By the arithmetic of the American Heart Association, the Masai should have been dropping on the plain. Mann put them through the machines. He took blood from hundreds and ran electrocardiograms on 400 young and middle-aged men, and in all of them found no evidence whatsoever of heart disease. Their cholesterol came back at about half the figure of an American of the same age. He put them on a step test and a treadmill and recorded a fitness he could only describe as Olympic standard: men who walked 20 miles a day behind cattle and would run alongside a vehicle for the fun of it. He went back and did the hard part. In 1972 he published autopsies on 50 Masai, and here is where the honest reader has to sit still, because it is the detail that makes the story. Their aortas showed atherosclerosis, plenty of it, lipid and fibrous change the whole length. And their coronary arteries were wide, far wider than an American's, and in none of the hearts was there a trace of a blockage, a scar or an infarct. They had the plaque and not the disease. The pipe had grown with the load. Whatever killed a Masai, and plenty did, it was not his milk. Mann came home a heretic and spent the rest of his career saying so in the journals, loudly, and the journals stopped printing him. The belief he had gone out to confirm is the belief still printed on the tub: that the fat of the animal is what stops a human heart. He took the best instruments of his age to the people who ate more of it than anyone alive, and the instruments said no, and the people were the fittest he had ever measured. The response of his profession was to find other populations. Four hundred men, half a doctor's expected cholesterol, zero disease, and a blood-and-milk breakfast. The science has had 60 years to answer that and has preferred to change the subject.

A New York physician who had spent twenty years failing to make fat people thin by starving them walked into the American Museum of Natural History, asked the curators what prehistoric man had eaten, and spent the next forty years prescribing fat meat and water to seventeen thousand patients. Blake Donaldson had done what every doctor did. He had put his heavy patients on low-calorie diets and watched them cheat, give up, or lose weight and put it back. So he went to look at the skulls. The teeth of our ancestors, the museum told him, were the teeth of meat-eaters, and the great weakness of the modern mouth was a sign that the diet had changed faster than the animal. Then an Arctic explorer, fresh from a year on meat in a New York hospital, told him that the Inuit lived well on fat and starved on lean. Donaldson built his prescription from that. Three meals a day of half a pound of fat meat each, three parts fat to one part lean by the calorie, salted, with water and black coffee, and a half-hour walk before breakfast. No flour, no sugar, no milk. His patients lost two to three pounds a week without hunger and kept it off. His allergy patients, he said, lost their allergies. He published it all in 1962 under the title Strong Medicine, with a line that is still quoted: there are probably only two perfect foods, fresh fat meat and clean water. The president of the American Medical Association's journal called the book unscientific. A Harvard nutritionist put it on a list of quackery that should be on nobody's shelves. That nutritionist was being funded by the sugar industry at the time, which emerged fifty years later. Donaldson died in 1966 having spent his whole career doing the one thing the establishment never managed: making his patients thin and keeping them that way. The establishment has spent the years since explaining why he should not have.

In 1991 eight people were sealed inside three acres of glass in the Arizona desert to prove that a carefully designed farm could feed humans without the outside world, and the design had almost no room in it for animals. Two years later the only thing inside that had reliably fed them was a handful of goats. Biosphere 2 cost a hundred and fifty million dollars. A rainforest, an ocean, a savannah and a farm under one roof, with the door welded shut for two years and nothing allowed in or out. The farm was the heart of it, and the farm was built on the modern idea: crops first, grown intensively, with livestock as an afterthought at the edges. A few African pygmy goats for milk, a flock of chickens, and four small feral pigs chosen because they could live on scraps. The pigs did not last the year. In a sealed box short of calories a pig is a competitor, and the crew killed and ate them. The chickens barely laid, because the glass cut the light and there was nothing to feed them that would make an egg. That left the goats, and for two years the goats were the only source of fat in a world designed around vegetables. The accounts the crew wrote afterwards return to them again and again. The half glass of milk a day was the thing people lived for. When a kid was born it was eaten and the meal was written up like a feast. The men lost nearly a fifth of their body weight, the women a tenth, and the food they dreamed of was never the sweet potatoes they had in abundance. It was the animal they had been given too few of. The plants were also taking the air. To make the crops grow the soil had been enriched with compost, and the microbes in that soil breathed oxygen faster than anyone had calculated. The level fell from twenty-one per cent to fourteen, the air of a high mountain, until the crew could not climb a staircase without resting and oxygen had to be trucked in from outside. The design that put plants first had removed the thing everyone needed most. Nobody has ever run the experiment the other way, with a herd at the centre and the crops at the edge. It would not have needed a doctor to explain the results. They were given three acres and told to feed themselves on plants. They ate the pigs, worshipped the goats, and suffocated.

People ask me why I'm so obsessed with ruminants. I've given it some thought, and my conclusion is that I'm not obsessed enough. A cow walks onto a wet hillside that grows nothing a human can eat, puts her head down, and comes back with steak, butter, cream and a pair of boots. She does it with a 150 litre fermentation tank she carries inside her, stocked with more bacteria than there have ever been people, which she feeds, waters and keeps at blood heat herself. Grass goes in. The bacteria take apart the one thing no animal can digest, and she lives on what they make. Then she digests the bacteria as well. Nothing is wasted. Even the fat comes out the far side rebuilt into something stable enough to fry in. Fuel: rain and sunlight. Emissions: next year's grass. She repairs herself, builds her own replacement every spring, and improves the ground she is standing on while she works. The finest engineers alive have spent billions trying to copy one chamber of her stomach in a steel shed, and so far they have made a paste. We have leaned on that machine for everything. The word capital comes from cattle, because a herd was the first bank. Domesday Book is written on sheep, and so was every deed in England for 500 years. Ruminants clothed our armies, lit our houses and carried our laws. Civilisation is a thing that happened to people who kept them. And they are such good company about it. A sheep remembers fifty faces for two years, which is forty-six more than I manage. A cow has a best friend, and her heart rate drops when that friend is beside her. A goat that cannot solve a problem will turn and look to you for help, as a dog does, and then ignore your advice. Let a herd out onto spring grass after a winter indoors and half a tonne of animal will skip. They ask for grass, rain, and to be left to get on with it. After ten thousand years of feeding, dressing and housing us, they will still walk over to the gate to see who you are. So no, I will not be calming down.

One of the founders of the Mayo Foundation ran a sanatorium for sixteen years in which he treated heart failure, kidney disease, high blood pressure, tuberculosis and obesity with one medicine: raw milk, several quarts a day, and nothing else. J. E. Crewe was not a crank. He was a physician at the most famous clinic in America, and the milk cure was an old treatment he had decided to take seriously. The patient went to bed. Every half hour through the day a glass of raw milk from grass-fed cows went down, up to four or five quarts, sometimes more. No other food. Weeks of it. He wrote it up in 1929 and the detail that stands out is the one that puzzled him most. He expected the swollen, waterlogged patients with failing hearts and kidneys to get worse on all that fluid. They did the opposite. The swelling went, the blood pressure fell, the urine cleared. One woman went from three hundred and twenty-five pounds to two hundred and eighty-four in a fortnight on four quarts a day, and her blood pressure came down fifty points with it. Diabetics improved. The tubercular gained weight. Nervous patients slept. Crewe said the treatment was so simple it was not interesting to the profession, and so effective it made him uncomfortable in his own clinic, because it suggested most of his colleagues' work was unnecessary. Pasteurisation came in, raw milk became a controlled substance, and the Mayo Clinic's own doctors stopped mentioning it. The article survives. The practice does not. The most prestigious hospital in America once put its sickest patients to bed with a glass of milk every half hour and watched them get well. It is now illegal to sell that milk in most of the states it was practised in.

The woman who taught Britain to cook on rations lived to 99, and the one thing she told the nation never to do was throw away the fat. Marguerite Patten was 24 when the war started and had been cooking for her family since her father died when she was 12. The Ministry of Food hired her. Her job was to go out to the factory canteens and the market squares with a demonstration stove and show a tired country how to make a dinner out of what the ration book allowed. Then she went on the wireless. The Kitchen Front, 5 minutes every morning after the news, with 7 million people listening. She was the voice that got a generation of mothers through the war. Here is what she actually taught. Save every scrap of dripping and use it for everything. Render the fat off the bacon. Keep the bones for stock. Make the meat ration go round with suet puddings and pies. She loathed the whale meat the Ministry made her demonstrate, and said so for the rest of her life. That generation came out of 14 years of rationing healthier than the one before it. The children were taller, the teeth were better, and nobody was fat. After the war she became the first cook on British television and wrote 170 books that sold 17 million copies. She refused the words celebrity chef to the end. She was a home economist, she said, and would die one. She died in 2015, aged 99, having outlived every diet fad of the century she had cooked through. Her advice was never about restriction. It was that the fat is the food, and a country that pours it away is wasting the best part of the animal. She was right in 1942 and she is right now.

In the early 1980s doctors in Cambridge laid premature babies on lambswool, and the babies grew faster. They were the smallest patients in the hospital. 34 infants, born weighing about two and a half pounds, lying in incubators. The standard bedding was a cotton sheet. A psychologist and a paediatrician had heard that mothers in Australia and New Zealand put newborns to sleep on lambskins, and that the babies seemed more settled. So they ran a proper trial. Half the babies were nursed on cotton. Half were nursed on a pad of lambswool. Nothing else was changed. The result went into the Lancet in 1983. The babies on wool put on 22.7 grams a day. The babies on cotton put on 18.6. That is nearly a quarter more growth, in children for whom every gram is a step away from danger, from changing what they lay on. Nobody was entirely sure why. Wool holds a layer of still, warm air against the skin. It takes up moisture without feeling damp. It gives under a body where a sheet does not. Hospitals had known a version of this for a long time. For decades a patient who was bedbound was put on a sheepskin to stop the skin breaking down, and trials in Australia later confirmed that real sheepskin prevents bedsores. Then came the synthetic version. A sheet of polyester pile that could be boiled and cost a fraction as much. It looked the part. It does not do the job. A ewe grows the best thing ever found for a newborn to lie on, and a lamb is born onto it. The hospital tested that against the alternative and wool won. The alternative was cheaper, so that is what most babies get.

In 1999 climbers found George Mallory's body high on Everest, 75 years after he vanished, and the clothes he died in were still on him. They were wool, silk and cotton. In 2006 somebody put on an exact copy and climbed the mountain in it. For decades the story had been that Mallory and Irvine were doomed by their kit. Tweed jackets and woolly jumpers at 28,000 feet. Brave amateurs, dressed for a grouse moor. The body told a different story. Mallory was wearing 8 thin layers. Silk next to the skin, then fine wool, then more silk, more wool, a flannel shirt, and a windproof cotton outer woven so tightly it turned the snow. Four British universities took fragments from the body and rebuilt the whole outfit, thread for thread. A mountaineer called Graham Hoyland wore it on Everest. He reported that it was warm. It was also lighter than the modern down suit his companions were wearing. The silk layers slid over the wool, so he could move his arms freely, which a man in a padded plastic suit cannot. The wool held its warmth when damp with sweat. He said he would have been comfortable going for the summit in it. The researchers concluded the clothing was fully up to the job. So the gear of 1924 was not the weak point. A sheep and a silkworm had solved the problem of the coldest place on earth, at less weight, before anyone had invented nylon. Then we spent a century replacing it with petroleum and told ourselves the men who came before were underdressed.

Try making sunflower oil at home and you'll understand everything wrong with seed oil. To make butter, you pour cream into a jar and shake it for ten minutes. To make dripping, you roast a joint of beef. It makes itself. To make olive oil, you crush olives and the oil runs out. To make sunflower oil, you squeeze a sunflower seed as hard as you like, and nothing comes out. Corn is about 4% fat. Nobody has ever bitten into a corn on the cob and had oil run down their chin. To get oil out of seeds like these, a factory crushes them, washes them in a petrol-based solvent, cooks the solvent off, treats the oil with caustic soda, bleaches it with clay, then steams it at around 240 degrees until it stops smelling. Every fat people ate for two million years could be made with your hands, a fire and a knife. Seed oil needs a chemical plant and a fire certificate. If your great-grandmother couldn't have made it in her kitchen, it has no business in yours.